132 Elementary Biology. 



develop inside the wall of the spore itself ; another and still 

 more striking example of one of the generalisations empha- 

 sised at the end of the preceding section, viz. that in the pro- 

 gress from lower to higher forms of plant life the importance 

 of the sexual thallus gradually diminishes as that of the 

 asexual plant gradually increases. Botanists are accustomed 

 to give names to these two generations. That bearing the 

 ovum is known as the oophyte, that bearing the spore as the 

 sporophyte. The oophyte and the sporophyte therefore 

 correspond to our thallus and asexual plant respectively. 

 The term gamophyte will be employed throughout in pre- 

 ference to oophyte, as taking into account both the male and 

 the female sexual organs. In the life-history of the moss, 

 therefore, the oophyte bears the sporophyte parasitic on it, 

 while in the fern, the oophyte (thallus) and sporophyte (fern 

 proper) are distinct plants. In Sf.lagirulla, the sporophyte 

 carries the oophyte for some time upon itself, and a con- 

 siderable part of its development is gone through in that 

 condition. 



Sporophyte. Let us now examine the sporophyte in 

 detail, and, taking the vegetative organs first, as in the last 

 type, we will consider it under the headings of stem, root, 

 and leaf, dealing subsequently with the asexual reproductive 

 organs, or sporangia. 



Stem. 'There are several striking differences between 

 the stem of Selaginella and that of Pteris. In-the first place, 

 it is almost entirely aerial and not underground. It is 

 cylindrical, long, and thin, and branches repeatedly in what is 

 known as the monopodial system, i.e. where the branch is a 

 lateral outgrowth from the principal axis, and not the result 

 of dichotomous division of the same (p. 84). The arrange- 

 ment of the branches, however, resembles that of Fucus in 

 that they are all on the same plane. The stem is very 

 slender, and consequently a considerable part of it rests on 

 the ground ; the primary part, indeed, may simulate the fern 

 rhizome in being underground. Moreover, its relationship 



